3,3'-[(2-chloro-5-methyl-p-phenylene)bis[imino(1-acetyl-2-oxoethylene)azo]]bis[4-chloro-N-(3-chloro-o-tolyl)benzamide]

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
see attached justification

Cross-reference

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

additional information on environmental fate and behaviour

Remarks:

Dispersion stability in simulated environmental media

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OECD 318

GLP compliance:

no

At any of the time points mentioned in the TG-318, the influence of Ca is critical. Regardless of pH, the pigment is categorized at the 24h-sampling time as “unstable” in 10 mM Ca, representing high water hardness.

After 6h, at pH 7 and 9 the samples showed high dispersion stability in 0 and 1 mM Ca. Stability at all other conditions was on the lower end of intermediate level

After 24 hours the stability for samples at pH 7 and 9 in 0 and 1 mM Ca became intermediate. For the samples at pH 4 and/or in 10 mM the stability was low.

Table 1: full results of the dispersion stability in the presence of NOM

	Ca(NO3)2	Stability after 6h	Standard deviation	Stability after 15h	Standard deviation	Stability after 24h	Standard deviation
	[mM]	[%]	[%]	[%]	[%]	[%]	[%]
pH 4	0	16.9	1.0	6.0	0.4	4.0	0.3
pH 4	1	10.3	1.1	4.4	0.9	3.3	0.7
pH 4	10	10.7	1.6	4.2	0.5	3.2	1.0
.
pH 7	0	93.7	1.6	86.0	4.2	76.8	1.9
pH 7	1	98.7	0.5	93.1	1.9	83.7	5.3
pH 7	10	13.9	1.4	6.6	1.2	3.7	0.1
.
pH 9	0	99.2	0.5	92.7	2.1	86.6	3.4
pH 9	1	98.0	0.7	81.3	0.8	48.9	0.9
pH 9	10	11.2	0.4	5.6	0.8	4.4	0.7

 

 

Cross-check the apparent stability by a fractionating method that physically separates particles from dissolved matter, and centrifugation results

 

To rationalize the observed dispersion stability, we finally checked the particle size distribution directly in the environmental medium (exact same sample preparation as for the UV/VIS measurements). We applied the NanoDefine method of Analytical Ultracentrifugation (SOP AUC-RI).

 

The observed size distributions confirm the moderate agglomeration at 1 mM Ca, pH7, with NOM. If the particles would have been significantly dissolved, no size distribution would be observable at all by this method, which relies on the detection of the movement of particles during centrifugal separation.

 

Additionally, the centrifugation methods include a determination of the remaining absorption after centrifugation, fully consistent with the conventional determination of the dissolved fraction after centrifugation as recommended by the TG-318. The remaining absorption was measured at c.a 0.014.This is a fraction of 0.7% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 0.7% of the sample may have been dissolved.

 

All evidence combined, the results after centrifugation confirm that at least 99.3% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Executive summary:

The dispersion stability of Pigment Yellow 93 depends especially on pH and water hardness. At pH 7 and 9 in 0 and 1 mM Ca stability is intermediate, at all other conditions (pH 4 and/or 10 mM Ca) the stability is low.